EP0310467B1 - Measuring devices comprising rheostat-type transducers - Google Patents

Description

The present invention relates to the field of measurement devices comprising a transducer of the rheostat type.

The present invention finds particular application in the design of measurement devices comprising a transducer of the rheostat type, intended for measuring the level and / or volume of the fuel in the tank of a motor vehicle.

Numerous devices have already been proposed for this particular application, comprising a mobile assembly provided with a float capable of monitoring the level of a liquid and associated with the cursor of a rheostat, so that the latter provides representative information. the position of the float and therefore the level and / or volume of liquid.

Rheostats have thus already been proposed formed from a support made of electrically insulating material coated with a track made of electrically resistant material, of controlled resistivity, on which the cursor associated with the moving equipment moves.

The rheostats of the aforementioned type have the disadvantage of having a drift over time, due to the inevitable wear of the controlled resistivity track, resulting from the friction caused by the movable cursor.

To eliminate this drawback, the Applicant has proposed and produced rheostats formed from a support made of electrically insulating material, in particular glass, coated with a first track made of electrically resistant material, of controlled resistivity, and of a plurality of second tracks separated, made of conductive material, connected with staggered to the resistive track and each extending opposite the path of movement of the cursor. The information representative of the level or volume of liquid is taken between one of the ends of the resistive track and the cursor.

The rheostats thus proposed by the Applicant have already rendered great services.

Document US-A-3614704 also describes a resistive measuring device comprising, on a support made of electrically insulating material, high resistance tracks and low resistance electrode sections in contact with the latter, in combination with a set of sliders. The set of cursors is rotated on the electrode sections. More specifically, the slider assembly is designed such that at least three sliders are simultaneously in contact with respective electrode sections. The purpose of the device proposed in document US-A-3614704 is to try to eliminate the drawbacks which may result from the wear of a cursor and / or of an electrode section. However, it has the following disadvantages. When the resistive measuring device of document US-A-3614704 is used as a rheostat, the resistance measured between the terminals of the rheostat varies substantially when one end of the three cursors which must rest against a respective electrode section is deficient. Similarly, when the resistive measuring device proposed in document US-A-3614704 is used as a potentiometer, part of the overall resistance of the potentiometer is theoretically short-circuited by the three cursors which must rest simultaneously on respective electrode sections. , but the short-circuited resistance part varies if one of the three cursors is deficient.

The present invention now aims to eliminate the drawbacks of the prior art and to improve the known devices by making them above all more reliable and more economical.

These aims are achieved in the context of the present invention by means of a measuring device comprising a transducer of the rheostat type, comprising in a manner known per se two cooperating assemblies, one formed by a movable cursor and the other by a support made of electrically insulating material coated with a plurality of main tracks extending opposite the path of movement of the cursor and having between them a controlled resistance, in which the cursor and each of the tracks have several contact elements respectively facing each other, and the contact elements of at least one of the two assemblies are offset relatively in the direction of movement of the cursor, so that when a contact element of the cursor is centered on the associated contact element of a formed track on the support, another contact element of the cursor is centered substantially on the interval formed between two contact elements which are there as associated with tracks made on the support, characterized in that the cursor and each of the tracks have two contact elements respectively facing each other, and the offset defined between two contact elements of the same set equals half the pitch of the main tracks .

This arrangement ensures permanent contact between the cursor and one of the tracks provided on the support, despite the discontinuity of these. The present invention therefore makes it possible to provide more reliable and more precise information as to the level or volume of liquid detected.

• ― la figure 1 représente une vue schématique en plan d'un dispositif conforme à un mode de réalisation préférentiel de la présente invention,
• ― la figure 2 représente une vue schématique de détail du même dispositif, et
• ― la figure 3 représente une variante de réalisation du dispositif conforme à la présente invention.

Other characteristics, objects and advantages of the present invention will appear on reading the detailed description which follows, and on examining the appended drawings, given by way of nonlimiting examples and in which:

• FIG. 1 represents a schematic plan view of a device according to a preferred embodiment of the present invention,
• FIG. 2 represents a schematic detail view of the same device, and
• - Figure 3 shows an alternative embodiment of the device according to the present invention.

We will first describe the preferred embodiment illustrated in Figures 1 and 2 attached.

We can see in Figure 1 attached a rheostat 10 comprising two assemblies, one bearing the general reference 20 formed by a lever 22 cursor holder, the other bearing the general reference 50 formed by a support 52 of electrically insulating material coated a plurality of main tracks 60, made of electrically conductive material, and an auxiliary track 70 made of electrically resistant material.

The support 52 is formed of a flat plate of electrically insulating material, for example ceramic, alumina or preferably glass.

Advantageously, the main tracks 60 are first deposited on the support 52, then the auxiliary track 70 made of electrically resistant material is subsequently deposited on the main tracks 60. The main tracks 60 and the auxiliary track 70 are preferably produced by screen printing deposit.

The lever 22 carrying the cursor is pivotally guided around an axis 23. The pivoting lever 22 is moreover provided, in a conventional manner per se, with a float (not shown in the appended figure for simplification of the illustration) suitable for monitor the fuel level in the tank of a motor vehicle.

The displacement of the above-mentioned float, depending on the fuel level, induces a pivoting of the cursor carrier lever 22 around the axis 23.

Two extreme positions of the pivoting lever 22 have been illustrated in FIG. 1 appended under the references 22 and 22 ′ respectively.

The cursor system carried by the lever 22 is placed opposite the main electrically conductive tracks 60.

More precisely still, according to a first characteristic of the present invention, the cursor system carried by the lever 22 comprises two contact elements 24, 26, that is to say two contact grains adapted to rest respectively against two elements of contact of the main tracks 60, that is to say two contact pads respectively associated formed at each of the main tracks 60.

These two contact pads are referenced 64, 66 in FIG. 2.

Furthermore, the path of movement of the contact grain 24 of the cursor is referenced 25 in FIG. 1 while the path of movement of the contact grain 26 of the cursor is referenced 27 in FIG. 1. Of course the paths 25 and 27 of the contact grains 24, 26 correspond to circular sectors centered on the pivot axis 23.

The main tracks 60 are juxtaposed and separated from each other. They are formed of generally rectilinear segments extending radially with respect to the pivot axis 23. In other words, the main tracks 60 generally consist of separate sectors, equidistant and of the same angular amplitude, with a centered crown. on the axis 23. The contact pad 64 cooperating with the contact grain 24 of the cursor is formed on the radially outer end of each main track 60. Conversely, the contact pad 66 cooperating with the contact grain 26 of the cursor is produced on the radially internal end of the main tracks 60.

The resistive auxiliary track 70 has the general shape of a continuous ring sector superimposed on the main tracks 60. The auxiliary track 70 is placed between the two contact pads 64, 66 of each main track 60. In other words, the mean radius of the auxiliary track 70 is between the radius of the contact pad 64 radially external and the radius of the range 66 radially internal.

The width (or radial extent) of the auxiliary track 70 is modulated (during screen printing) to define an evolution of the resistance of the auxiliary track 70 taking into account the geometry of the reservoir.

In addition, connection tracks 80 made of electrically conductive material are deposited on the support 52. The connection tracks 80 extend certain selected main tracks 60.

The connecting tracks 80 can be produced simultaneously or after the main tracks 60.

Some of the connecting tracks 80 connected to the main main tracks 60 of the rheostat allow the total resistance of the auxiliary track 70 and / or the resistance defined between one of the ends of the auxiliary track 70 and the cursor to be measured.

The other connecting tracks 80 connected to intermediate main tracks 60 are connected in pairs to electrically resistant elements 82. These are advantageously produced by screen printing simultaneously with the auxiliary track 70. The elements 82 are thus connected in parallel with sections determined from the auxiliary track 70. The elements 82 can be adjusted by laser to precisely adjust the overall resistance of corresponding section of the rheostat, in order to eliminate manufacturing dispersions.

During the aforementioned adjustment of the elements 82, using a laser, the resistance at the terminals of these elements (and therefore at the terminals of the corresponding sections of the rheostat) is measured at the level of conductive pads 84 connected to the terminals of the elements 82 The elimination of manufacturing dispersions using adjustable elements 82 is conventional in itself and will not be described in more detail below.

We will now describe with more precision, with reference to FIG. 2 appended, the geometry of the main tracks 60 electrically conductive deposited on the insulating support 52, in accordance with a preferred embodiment of the present invention.

According to this preferred embodiment, the areas 64, 66 of each of the main tracks 60, cooperating respectively with the pads 24, 26 of the cursor, are each formed of a crown sector centered on the pivot axis 23, and s 'therefore extending radially with respect thereto. However, the contact pads 64, 66 of the same main track 60 are angularly offset with respect to each other by a value equal to half a step of the main tracks 60, while the two contact elements 24 , 26 of the cursor are placed on the same radius centered on the axis 23.

In the appended FIG. 2, reference has been made to the angular pitch of the main tracks 60 at the level of the contact pads 66 radially internal. The angular offset existing between a radially external contact pad 64 and a radially internal contact pad 66 of the same main track 60 has been referenced B. Finally, the angular pitch of the main tracks 60 is referenced C at the pads of contact 64 radially external.

To meet the aforementioned provisions, the angular pitch A at the radially internal pads 66 is equal to the angular pitch C at the radially outer pads 66. In addition, the angular difference B between the radially external contact pads 64 and the radially internal contact pads 66 equals half of the aforementioned angular steps A and C.

Likewise, in the appended FIG. 2, reference 28 is made to the common radius centered on the contact grains 24, 26 and passing through the pivot axis 23.

Those skilled in the art will readily understand that, thanks to the aforementioned provisions, when one of the contact elements of the cursor (24 or 26) is centered on the associated contact element (64 or 66) of a track 60 formed on the support 52, the other contact element (26 or 24) of the cursor is centered substantially on the gap formed between two contact elements (66 or 64) associated therewith with tracks 60 formed on the support.

The width of the contact elements 24, 26 (the diameter in the case of circular contact grains 24, 26) is greater than the interval separating two contact pads 64 or 66 from adjacent tracks 60. Thus, the two contact elements 24, 26 each remain permanently in contact with at least one of the tracks 60. This arrangement makes it possible to obtain reliable information despite the discontinuity of the tracks 60.

According to another advantageous characteristic of the invention, the interval d formed between two contact pads 64 radially external and adjacent equals the interval d formed between two contact pads 66 radially internal and adjacent.

For this, the tracks 60 are delimited by non-radial longitudinal edges.

More precisely still, preferably, each of the contact pads 66, 64 is delimited by longitudinal edges which extend parallel to spokes erected from the pivot axis 23 and passing through the middle of the interval defined between two adjacent contact pads.

We see in Figure 2 three main tracks 60a, 60b and 60c, juxtaposed.

The adjacent longitudinal edges 90 and 91 delimiting the radially external contact pads 64 of the two tracks 60a, 60b are parallel to the radius 92 passing through the middle of the interval defined between these two contact pads 64. Similarly, the adjacent longitudinal edges 93 and 94 delimiting the contact pads 64 radially external of the two tracks 60b and 60c are parallel to the passing radius 95 by the middle of the interval defined between these two contact pads 64.

Similarly, the two adjacent longitudinal edges 96, 97 delimiting the contact pads 66 radially internal to the tracks 60a, 60b are parallel to the radius 98 passing through the middle of the interval d defined between these two contact pads 66. Similarly the longitudinal edges 99 and 100 adjacent defining the radially internal contact areas 66 of the tracks 60b and 60c extend parallel to the radius 101 passing through the middle of the interval defined between these two contact areas 66.

To this extent the radially external contact pads 64 and the radially internal contact pads 66 of each main track 60 are connected by a strip 68 inclined with respect to spokes drawn from the axis 23. Preferably, these strips 68 are formed on the outside of the resistive auxiliary track 70, that is to say in a position adjacent to the contact pads 64 radially external.

• ― la plaque support 52 est réalisée en alumine,
• ― il est prévu 96 pistes principales 60. Celles-ci sont formées de segments s'étendant généralement radialement par rapport à l'axe de pivotement 23. Le pas des pistes angulaires 60 est de l'ordre de 1°. Au niveau de leur extrémité radialement la plus interne les pistes principales 60 ont une largeur de l'ordre de 0,2 mm et l'espacement entre deux pistes 60 adjacentes est de l'ordre de 0,2 mm. La longueur radiale des pistes 60 est de l'ordre de 8 mm. Les pistes 60 sont réalisées par sérigraphie à base d'une pâte électriquement conductrice du type Pd/Ag, telle que la pâte commercialisée par la Société Dupont De Nemours sous la référence 9473,
• ― la piste auxiliaire résistive 70 est réalisée par dépôt sérigraphique. Elle est continue et s'étend sous forme d'un secteur de couronne, centrée sur l'axe de pivotement 23, entre les plages de contact 64 et 66. Sa largeur radiale est de préférence modulée, comme illustré sur la figure 1 annexée, en fonction de la géométrie du réservoir, de telle sorte que l'information prélevée, (i.e. la mesure de la résistance entre une extrémité de la piste 70 et le curseur) soit toujours proportionnelle au volume de liquide contenu dans le réservoir. La piste auxiliaire 70 peut être réalisée à l'aide d'une pâte électriquement résistante à base d'oxyde de ruthénium, par exemple la pâte commercialisée par la Société Dupont de Nemours sous la référence 1613,
• ― les grains de contact 24, 26 du curseur, reposant respectivement contre les plages de contact 64 et 66 sont réalisés à base d'un alliage Ag/Ni.

According to an embodiment currently considered preferential, but given by way of nonlimiting example, the rheostat conforming to the present invention meets the following characteristics:

• The support plate 52 is made of alumina,
• - 96 main tracks 60 are provided. These are formed by segments generally extending radially relative to the pivot axis 23. The pitch of the angular tracks 60 is of the order of 1 °. At their radially innermost end, the main tracks 60 have a width of the order of 0.2 mm and the spacing between two adjacent tracks 60 is of the order of 0.2 mm. The radial length of the tracks 60 is of the order of 8 mm. Tracks 60 are produced by screen printing based on an electrically conductive paste of the Pd / Ag type, such as the paste sold by the Dupont De Nemours company under the reference 9473,
• - the resistive auxiliary track 70 is produced by screen printing. It is continuous and extends in the form of a crown sector, centered on the pivot axis 23, between the contact pads 64 and 66. Its radial width is preferably modulated, as illustrated in the appended FIG. 1, as a function of the geometry of the reservoir, so that the information collected (ie the measurement of the resistance between one end of the track 70 and the cursor) is always proportional to the volume of liquid contained in the reservoir. The auxiliary track 70 can be produced using an electrically resistant paste based on ruthenium oxide, for example the paste sold by the Dupont de Nemours company under the reference 1613,
• - The contact grains 24, 26 of the cursor, resting respectively against the contact pads 64 and 66 are made from an Ag / Ni alloy.

According to the preferred embodiment illustrated in FIGS. 1 and 2 appended and previously described, the pads 64, 66 of the same track 60 have an angular offset corresponding to the half-step of the tracks, while the contact elements 24, 26 of the cursor are placed on the same radius.

There is illustrated in FIG. 3 appended an alternative embodiment according to which, on the contrary, the contact elements 24, 26 of the cursor have a relative angular offset corresponding to the half-pitch of the tracks 60, while these are formed of straight sectors s extending radially with respect to the pivot axis 23.

In other words, according to the variant embodiment illustrated in the appended FIG. 3, the contact pads 64, 66 of the same track 60, are centered on a common radius drawn up from the pivot axis 23. By against, the contact element 24 of the cursor is centered on a radius 30 while the contact element 26 of the cursor is centered on a radius 32. The angular distance B ′ between the spokes 30 and 32 corresponds to half the angular pitch A ′ defined between tracks 60, that is to say between two contact pads 64 radially external and adjacent and / or two contact pads 66 radially internal and adjacent.

Those skilled in the art will readily understand that, thanks to the variant embodiment illustrated in appended FIG. 3, the same is obtained as when one of the contact elements of the cursor 24 or 26 is centered on the associated contact element 64 or 66 of a track 60 formed on the support 52, the other contact element 26 or 24 of the cursor is centered substantially on the gap formed between two contact elements 66 or 64 which are associated with it tracks 60 formed on the support.

Preferably, in the context of the variant embodiment illustrated in FIG. 3, the interval d formed between two contact pads 64 radially external and adjacent remains identical to the interval d formed between two contact pads 66 radially internal and adjacent . For this, the longitudinal edges of the tracks 60 extend parallel to spokes erected from the pivot axis 23 and passing through the middle of the intervals defined between two adjacent tracks 60. In addition, the resistive auxiliary track 70 is also deposited between the radially external contact pads 64 and the radially internal contact pads 66.

Of course the present invention is not limited to the particular embodiments which have just been described but extends to all variants in accordance with its spirit.

If necessary, one of the two contact elements of the cursor 22 can be adapted to cooperate with a minimum level detection and alert generation track, when the cursor is placed in a range of its movement corresponding to a level minimum fuel in the tank of a motor vehicle.

Claims (10)

1. Measuring device having a rheostat-type transducer comprising two cooperating assemblies, one formed by a movable pointer (22) and the other by a support (52) of electrically insulating material coated with a plurality of main tracks (60) extending opposite the path of travel of the pointer and having between them a monitored resistor, in which device the pointer (22) and each of the tracks (60) have a plurality of respectively opposite contact elements (24, 26; 64, 66), and the contact elements of at least one of the two elements are relatively offset in the direction of travel of the pointer such that when a contact element (24, 26) of the pointer is centred on the associated contact element (64, 66) of a track (60) made on the support, another contact element (26, 24) of the pointer is centred substantially on the interval made between two contact elements (66, 64) associated with it of the tracks made on the support (52), characterized in that the pointer and each of the tracks have two respectively opposite contact elements, and the offset (B) defined between two contact elements (24, 26; 64, 66) of a single assembly equals half the pitch (A) of the main tracks (60).

2. Measuring device according to Claim 1, characterized in that the pointer (22) is rotatably movable, and in that the two contact elements (24, 26; 64, 66) of each assembly are provided at different spacings from the axis of rotation (23).

3. Measuring device according to one of Claims 1 to 2, characterized in that the main tracks extend substantially radially with respect to the axis of pivoting (23).

4. Measuring device according to one of Claims 1 to 3, characterized in that the same space (d) is provided between the two rows of contact elements (64, 66) provided on the insulating support (52).

5. Measuring device according to one of Claims 1 to 4, characterized in that the main tracks (60) are made of an electrically conductive material, preferably by screen printing, and in that a secondary track (70) of electrically resistive material is placed on top of the main tracks (60), preferably by screen printing.

6. Measuring device according to Claim 5, characterized in that the resistive secondary track (70) is placed between two contact elements (64, 66) of a single main track (60).

7. Measuring device according to one of Claims 1 to 6, characterized in that the two contact elements (64, 66) of each main track (60) have a relative angular offset (B) equal to half the angular pitch (A) of the tracks, while the two contact elements (24, 26) of the pointer are centred on a single radius.

8. Measuring device according to Claim 7, characterized in that the two contact elements (64, 66) of each main track (60) are formed by contact zones extending radially opposite the axis of rotation of the pointer, and are connected to one another by a non-radial connection strip (68).

9. Measuring device according to one of Claims 1 to 6, characterized in that the pointer comprises two contact elements (24, 26) having a relative angular offset (B′) equal to half the pitch (A′) of the main tracks (60), while the latter are formed by rectilinear segments extending radially with respect to the axis of pivoting (23) of the pointer.

10. Measuring device according to one of Claims 1 to 9, characterized in that the contact elements (24, 26) of the pointer have a width greater than the interval (d) defined between two adjacent associated contact elements (64, 66) defined at the level of main tracks, such that each contact element of the pointer remains permanently in contact with at least one of the main tracks (60).

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